A liquid crystal display device is used in various fields of OA equipments such as a personal computer and a television set, taking advantage of the features such as light weight, thin shape, and low power consumption. In recent years, the liquid crystal display device is used also as displays for a portable remote terminal such as a cellular phone and PDA (personal digital assistant), a car navigation equipment, and a game machine.
In the process for manufacturing the liquid crystal display device, the measure against electrostatic is indispensable. For example, there is a possibility that various wirings in an active area, a switching element, etc., are damaged with static electricity generated in the manufacturing process, or invaded from outside. The technique for improving tolerance over such static electricity is examined variously.
For example, a structure equipped with a dummy poly-silicon semiconductor layer in each pixel is proposed different from the poly-silicon semiconductor layer constituting a thin film transistor. A gate electrode line overlaps with the poly-silicon semiconductor layer and the dummy poly-silicon semiconductor layer through a gate insulating film. In such structure, a process until forming the gate electrode line is conducted under following conditions. That is, when a substrate is placed on a table, capacitance formed between the poly-silicon semiconductor layer and the table is set to Ca, capacitance formed between the poly-silicon semiconductor layer and the gate electrode line through the gate insulating film is set to Cb, capacitance formed between the dummy poly-silicon semiconductor layer and the table is set to Cc, capacitance formed between the dummy poly-silicon semiconductor layer and the gate electrode line through the gate insulating film is set to Cd, the dummy poly-silicon semiconductor layer is formed to satisfy an equation: Ca/(Ca+Cb)<Cc/(Cc+Cd). According to the above structure, a voltage impressed to the gate insulating film between the dummy poly-silicon semiconductor layer and the gate electrode line becomes larger rather than the voltage impressed to the gate insulating film between the poly-silicon semiconductor layer and the gate electrode line. For this reason, even if it is a case where electric charges are accumulated to the extent that electrostatic discharge destruction takes place in the gate insulating film between the poly-silicon semiconductor layer and the gate electrode line, and between the dummy poly-silicon semiconductor layer and the gate electrode line, breakdown of the gate insulating film between the dummy poly-silicon semiconductor layer and the gate electrode line generates preferentially, and the thin film transistor equipped with the poly-silicon semiconductor layer is protected.
By the way, in the recent liquid crystal display device, requests for a high definition display and a high aperture ratio has been increasing. Accordingly, it becomes difficult to keep a space to arrange the dummy poly-silicon semiconductor layer in each pixel.